The greatly increased use of bicycles, pedal-operated exercisers and the like has led to a strong demand for better and more efficient drives for such devices. The traditional direct drive on bicycles between pedal cranks and the chain driving sprocket has the inherent disadvantage of unequal torque development at and near pedal crank dead center positions. At such positions, downward thrust on the pedals is substantially diminished as is the production of torque at the chain drive wheel or sprocket, and this is a cyclical condition in standard bicycle drives and the like.
It is the objective of the invention to overcome this problem of non-uniform torque development in drives for bicycles and similar machines to the greatest possible degree. More particularly, it is the aim of the invention to cause the pedal cranks to retard and advance with respect to the chain driving sprocket by varying the instantaneous gear ratio between the pedal cranks and chain sprocket. This cyclical change in gear ratio and resulting mechanical advantage partially compensates for the inherent cyclical disadvantage at and near pedal crank dead center positions. By means of the invention, a much more uniform torque is developed at the chain driving sprocket.
In the invention, the variations in mechanical advantage repeat twice within the cycle of one complete revolution, and the pedal cranks complete the same number of revolutions as does the chain wheel or sprocket over a given period of time.
The construction of the invention is such that simple or complex non-circular gears may be used to generate the desired cyclical changes in mechanical advantage. The center-to-center distance between the gear shafts remains constant and the instantaneous sum of the effective pitch radii of the gears at the point of engagement will equal this center distance. The ratio of the instantaneous pitch radii determines the instantaneous mechanical advantage of the gear set. The product of this instantaneous ratio and that of the other gear set determines the overall ratio. If the gears are identical, the square root of the overall ratio is accomplished in each gear set. In a complete revolution, the pedal cranks will cycle through a speed ratio of: PA4 1:1--same PA4 &gt;1:1--advance PA4 1:1--same PA4 &lt;1:1--retard PA4 1:1--same PA4 &gt;1:1--advance PA4 1:1--same PA4 &lt;1:1--retard PA4 1:1--same (starting point)
relative to the chain wheel.
To satisfy the requirements for disclosure of known prior art under 37 C.R.F. 1.56, the following United States patents are made of record herein: U.S. Pat. Nos. 540,189 550,206 623,863 653,873 703,613 2,184,049 3,865,366 3,899,932.
Also, the following article is made of record: "The Effects of Circular and Elliptical Chainwheels on Steady-Rate Cycle Ergometer Work Efficiency", Henderson et al., Medicine and Science in Sports, Vol. 9, No. 4, pp. 202-207 (1977).